Redox Practice

In the reaction
2Ca(s) + O₂(g) --> 2CaO(s), calcium is __________

• Reduced

• Synthesized

• Oxidized

• None of the above

Answer explanation

In the reaction, calcium (Ca) loses electrons to form CaO, indicating it is oxidized. Oxidation involves the loss of electrons, which is the case here, making 'oxidized' the correct choice.

Tags

NGSS.HS-PS1-2

     In the reaction Zn + H₂O --> ZnO₂ + H₂
 which element, if any, is oxidized? 

• Zinc

• Hydrogen

• Oxygen

• None

Answer explanation

In the reaction, zinc (Zn) is oxidized as it loses electrons to form ZnO₂. Hydrogen (H₂O) is reduced, while oxygen is not oxidized. Therefore, the correct answer is Zinc.

Tags

NGSS.HS-PS1-2

What substance is being oxidized in the following reaction? 
Fe⁺² + MnO₄-->  Fe⁺³ + Mn⁺²   

• Fe⁺²

• Mn⁺³

• Mn⁺²

• MnO₄

Answer explanation

In the reaction, Fe⁺² is oxidized to Fe⁺³, losing an electron. MnO₄ is reduced to Mn⁺². Therefore, the substance being oxidized is Fe⁺².

Tags

NGSS.HS-PS1-2

Is calcium oxidized or reduced in the following reaction? 
2CaO--> 2Ca + O₂

• Oxidized

• Reduced

Answer explanation

In the reaction 2CaO -> 2Ca + O2, calcium (Ca) goes from a +2 oxidation state in CaO to a 0 oxidation state in elemental Ca. This decrease in oxidation state indicates that calcium is reduced.

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

N₂ +O₂ --> 2NO
Determine which substance is oxidized and which is reduced.

• Nitrogen is oxidized and Oxygen is reduced. 

• Nitrogen is reduced and Oxygen is oxidized. 

Answer explanation

In the reaction, nitrogen (N2) increases its oxidation state from 0 to +2 in NO, indicating it is oxidized. Oxygen (O2) decreases its oxidation state from 0 to -2 in NO, indicating it is reduced. Thus, nitrogen is oxidized and oxygen is reduced.

Tags

NGSS.HS-PS1-2

In reduction, atoms or ions

• increase their oxidation number.

• decrease their oxidation number.

• do not change their oxidation number.

• have a zero oxidation number after the reaction.

Answer explanation

In reduction, atoms or ions gain electrons, which results in a decrease in their oxidation number. Therefore, the correct answer is that they decrease their oxidation number.

Tags

NGSS.HS-PS1-1

Use oxidation numbers to determine the element oxidized and reduced in the following reaction:

HNO₃ + H₂S → NO + S + H₂O

Oxidized: ​ (a)  

Reduced: ​ (b)  

• N

• H

• O

• S

Answer explanation

In the reaction, sulfur (S) is oxidized from -2 in H2S to 0 in S, while nitrogen (N) is reduced from +5 in HNO3 to +2 in NO. Thus, S is oxidized and N is reduced.

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

In the reaction 2Fe²⁺ + Cl₂ → 2Fe³⁺ + 2Cl^-, which species is reduced?

• Cl^-

• Fe³⁺

• Cl₂

• Fe²⁺

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

Which statement is true about redox reactions?

• Oxidation and reduction always occur together.

• Only oxidation occurs in redox reactions.

• Only reduction occurs in redox reactions.

• Neither oxidation nor reduction occurs in redox reactions.

Tags

NGSS.HS-PS1-7

Which of the following best describes oxidation in a chemical reaction?

• Gain of electrons

• No change in oxidation number

• Loss of electrons

• Decrease in oxidation number